EWSR1 and cancer: It seems, however, that ‘unclassifiable' EWSR1-rearranged neoplasms represent only a small proportion of cases in this study; from these relatively small numbers there were no identifiably recurrent morphologic patterns or immunoprofiles, so the hypothesis of these representing malignant tumours in which EWSR1 rearrangement was present due to inherent genetic instability rather than as a driver mechanism for pathogenesis appears more likely.